Formation of droplets of shear‐thinningnon‐Newtonianfluids in a step‐emulsification microdevice

Abstract

In this paper, the formation mechanism of droplets of shear-thinning non-Newtonian fluids in a step-emulsification microdevice is studied experimentally, by using aqueous solutions of sodium carboxymethyl cellulose (CMC) as the dispersed phase and cyclohexane as the continuous phase. According to the evolution of the front-end length of the dispersed thread over time, the droplet generation process is divided into three stages: the two-dimensional expansion stage, the three-dimensional rapid expansion stage, and the necking stage. The influence of the dispersed phase flow rate Q d and CMC concentration c on droplet formation is described. The results show that the addition of CMC in the aqueous solution increases the viscosity of the dispersed phase and slows down the evolution of the dispersed phase, thereby resulting in the increase of the droplet size. Finally, a droplet volume prediction model considering non-Newtonian characteristics is proposed, and the formation of satellite droplets is analyzed.

Accelerating Effects of Flow Behavior Index n on Breakup Dynamics for Droplet Evolution in Non-Newtonian Fluids

“…For the previous research, H(λ) was a certain value in the Newtonian fluid related to the two-phase viscosity ratio λ [42], or in the non-Newtonian fluid related to the mass fraction wt [21,22]. The equations in Table 3 with different |n| also proved H(λ) being a certain value.…”

“…Aqueous solutions of NaAlg with different mass fractions were used as the dispersed phase, which were demonstrated as shear-thinning non-Newtonian fluids. The commonly used models to describe the flow behavior of shear-thinning fluids were the power-law [21,22] or Ostwald de Waele model [23,24], Bird-Carreau, Herschel-Bulkley models, etc. In figure 2, the experimental data agree well with the predicted values of the Bird-Carreau model, and the relationship between the fluid viscosity η and the shear rate γ could be expressed as [25][26][27] The commonly used models to describe the flow behavior of shear-thinning fluids were the power-law [21,22] or Ostwald de Waele model [23,24], Bird-Carreau, Herschel-Bulkley models, etc.…”

“…The commonly used models to describe the flow behavior of shear-thinning fluids were the power-law [21,22] or Ostwald de Waele model [23,24], Bird-Carreau, Herschel-Bulkley models, etc. In figure 2, the experimental data agree well with the predicted values of the Bird-Carreau model, and the relationship between the fluid viscosity η and the shear rate γ could be expressed as [25][26][27] The commonly used models to describe the flow behavior of shear-thinning fluids were the power-law [21,22] or Ostwald de Waele model [23,24], Bird-Carreau, Herschel-Bulkley models, etc. In Figure 2, the experimental data agree well with the predicted values of the Bird-Carreau model, and the relationship between the fluid viscosity η and the shear rate γ could be expressed as [25][26][27]:…”

“…Figure 6 plotted the relationship between the minimum neck width wm and the remaining time T − t within one period time T by the data processing from Figure 5. The formation and breakup of NaAlg micro-droplets in one period could be separated for three stages [22,[28][29][30], which were the growth stage(T − t > 270 ms), the squeezing stage(20 ms < T − t < 270 ms), and the pinch-off stage(T − t < 20 ms). In Figure 6, the data in growth, squeezing, and pinch-off stages were signed by the colors of blue, red, and black, respectively.…”

Formation of viscoelastic droplets in a step‐emulsification microdevice

“…The evolution speed of the dispersed phase with time is basically unchanged and does not change with the change of PEO concentration and molecular weight, but it increases with the increase of the dispersed phase flow rate. The changes of the two‐dimensional expansion process with operating conditions indicate that this is a simple fluid injection process, 31 which is not affected by the physical properties of the dispersed phase such as viscoelasticity, and is only determined by the injection flow rate of the dispersed phase.…”